Reciprocating piston engine and ported piston for use therein



WILD

Jan. 8, 1963 PISTO N F0 RECIPROCATING N ENGINE AND PORTED PISTO R USE THEREIN Filed Sept. 22, 1961 INVENTOR [kw/M @617. #8221 ATTORNEY-S MMM;W%

United States Patent 3 071 921 RECIPROCATING rrsioN ENGINE AND roman 1 PrsroN FOR USE THERErN Frederick G. Wild, 6 Crater Place, Alexandria, Va. Filed Sept. 22, 1961, Ser. No. 140,021 16 Claims. 01. 60-6) This invention relates generally to the art of reciprocating piston engines. More specifically, the invention is directed to an improved reciprocating piston engine, its operation and, in particular, a piston construction for use therein. Under the teaching of the invention, exhaust gases that are normally discharged from a reciprocating piston engine while still containing a measure of potential energy are employed to assist in driving the piston to achieve increased efliciency of the engine in converting gaseous fluid energy into usable work output from the engine.

As used herein, the terms gas, gaseous fluid or gaseous motive fluid are intended to embrace all motive fluids such as combustion products, steam, air, etc., which may be employed in driving a reciprocating piston engine. Although embodiment of the invention in an internal combustion engine of the gasoline type is specifically described and illustrated on the drawing, the invention is equally applicable to steam engines, air engines, etc., and thus may be adapted to the general class of engines wherein a reciprocating piston is acted upon by a gaseous fluid medium to drive the piston in converting potential energy in the form of heat and pressure into useful work as the engine output.

The advantages flowing from the instant invention may be pointed up by reference to the operation of a conventional internal combustion engine. This type of engine as an example, has reached a fairly high state of development and perfection. In operation of such engines, it has long been accepted that the exhaust valve in the engine should be opened before the piston reaches the bottom of its stroke to release the exhaust gases from the cylinder bore chamber and lower the pressure for the exhaust stroke that follows. Thus these exhaust gases are released while they are still at super-atmospheric pressure and, therefore, still contain a measure of usable energy which is discarded through the exhaust port. This characteristic operation results in rapid flow of the gases through the exhaust port, and in the great majority of instances where engine noise would be objectionable, requires the use of inuffiing arrangements to reduce the engine noise and release the exhaust gases, as quietly as possible.

The exhaust gases under super-atmospheric pressure at the moment of opening the exhaust valve, contain a measure of potential energy in the form of their pressure and elevated temperature. This energy possibly including some unburned fuel in the conventional internal combustion engine is dissipated, a part of it being used to force the gases past the exhaust valve and through the exhaust port, and a further portion being dissipated in the mufiler that is considered necessary to minimize the noise that would result from the operation of an unmuffled engine.

Recognizing the potential energy that is dissipated and lost in the conventional disposition of exhaust gases in an internal combustion engine as outlined above, and also recognizing that this loss of potential energy is characteristic of various types of reciprocating piston engines, the instant invention has as its principal object the provision of a reciprocating piston engine wherein improved efiiciency in utilization of the energyin the gaseous motive fluid is achieved by conversion of a greater portion of such energy into useful work as output from the engine.

3,071,921 Patented Jan. 8, 1963 "r ce It is another object of the invention to provide an improved reciprocating piston engine which utilizes the en ergy remaining in the gases normally exhausted While at super-atmospheric pressure and elevated temperature to assist in driving the piston of the engine.

Another object of the invention is to provide a reciproeating piston engine, operable at increased efficiency in conversion of energy in a gaseous motive fluid into useful work, having a piston provided with at least one passage therethrough to receive the exhaust gases, expand them, and direct the expansion of such gases in the form of a jet to impart a reaction force to the piston by flow of the exhaust gases through the passage, such reaction forces acting to assist in driving the piston.

A further object of the invention is to provide a reciprocating piston engine of the four cycle internal combustion type wherein each piston therein is provided with at least one passage for expanding and directing the exhaust gases to impart a reaction force to the piston assisting in driving the piston and wherein valving means operable in timed relation with the speed of engine operation is provided to open said passage shortly before the piston reaches the bottom of its stroke on the power stroke of engine operation.

It is also an object of the instant invention to provide a piston construction for incorporation in a reciprocating piston engine, which piston has a passage therethrough disposed to conduct exhaust gases from the cylinder bore of the engine, and expand such gases in a direction to create a force assisting in driving movement of the piston.

Briefly, the advantages of the instant invention are achieved by providing a reciprocating piston engine wherein the piston reciprocable within the engine cylinder bore is provided with a passage, one end of which communicates with the interior of the cylinder bore chamber to receive and carry away exhaust gases therefrom. The piston passage has an exit portion immediately preceding its outlet, with such exit portion expanding in cross sectional area toward the outlet, and with this portion being directed to extend laterally and generally toward the cylinder bore chamber while exiting at a point removed from the chamber. Thus the exhaust gases 'within the cylinder bore chamber, when vented through the passage as the piston nears the outer end of its power stroke, are expanded within the passage, thereby creatinga velocity flow of the gases, which flow is directed such that a force assisting in driving the piston results.

Before turning to a specific description of a particular application of the invention as illustrated on the accompanying drawing, it may be well to further point out the areas of use of the instant invention and advantageous features flowing from such use. As heretofore noted, the invention is applicable to various types of reciprocating piston engines employing a gaseous motive fluid such as steam, air and products of combustion. With reference to internal combustion engines, either gasoline or diesel, the invention may be applied-in such engines of either the four cycle or two cycle type.

More specific advantages which may be pointed out as attendant to use of the instant invention include the fact that increased power for a given energy input may from the cylinder bore at a lower average pressure and more uniform rate, thereby permitting the use of less baffling in the muffling system to control noise.

Additionally, an engine constructed in accordance with the instant invention may experience less vibration in engine operation since the exhaust gases flow smoothly through the piston passage maintaining a positive downward pressure on the piston rather than being exhausted abruptly in a direction opposite to piston movement through the conventional exhaust valve. In this respect, there are indications that the abrupt opening of the exhaust valve in the conventional internal combustion engine thereby relieving the exhaust gases from the top of the cylinder bore causes an instantaneous application of a negative pressure on the piston as it nears the bottom of its power stroke. This negative pressure abruptly resists continued downward movement of the piston while the crank shaft continues its rotary movement, thus not only imparting a vibration to the engine, but also imparting a strain on the bearings at the ends of the connecting rod. Accordingly, the engine of this invention may achieve an increase in bearing life for the wrist pin and crank pin bearings.

The above mentioned objects and advantages and other more specific objects and novel features of the instant invention will be apparent from the following description taken in conjunction with the accompanying drawing. It is to be expressly understood, however, that the drawing is only for the purpose of illustration, and in no way is intended to define the limits of the invention. The drawing merely illustrates in somewhat diagrammatic form an adaptation or embodiment of the invention in a reciprocating piston engine.

The single FIGURE on the drawing is a sectional view, diagrammatically illustrating an adaptation of the instant invention to a generally typical internal combustion engine of the four cycle gasoline type.

Referring to the drawing, a portion of an engine cylinder block is shown with a bore 11 formed therein. This bore retains a sleeve 12, the interior of which forms the cylinder bore for the reciprocating piston. The upper end of the sleeve 12 is closed by a cylinder head 13, such that a cylinder bore chamber 14 is formed by the interior of sleeve 12 and the portion of head 13 which closes the upper end of sleeve 12. A piston 15, specifically constructed in accordance with the instant invention, is reciprocally mounted within the cylinder bore.

It will be appreciated that the head 13 is suitably secured to the block 10 as by means of conventional cylinder head bolts (not shown), such that chamber 14 is defined within sleeve 12 above piston 15 for containing the gaseous motive fluid while it is acting on piston 15 to drive it downwardly. The engine diagrammatically shown on the drawing is shown provided with an inlet valve mounted in head 13 to control the supply of combustible mixture to the cylinder bore chamber 14 through duct 21. Similarly, a generally conventional exhaust valve 22 is shown mounted in head 13 to be operable in release of spent gases from chamber 14 to flow out through exhaust duct 23 as the piston 15 rises.

It will be understood that the inlet valve 20 and exhaust valve 22 are to be appropriately actuated by cams mounted on a cam shaft in accordance with well known engine practices. The structure of such cams and cam shaft, driven in timed relationship with the speed of operation of the engine, are not shown since their specific construction is not important with regard to the instant invention.

It may be mentioned that the operation of the inlet valve 20 can be carried out in accordance with conventional practice in the operation of a four cycle internal combustion engine, whereas the opening and closing of the exhaust valve 22 by its actuating cam will be slightly different from that found in conventional practice. As Will be more apparent from subsequent description, the exhaust valve is provided solely to vent gas which remains above the piston when the piston starts up from the bottom of the power stroke. Thus the exhaust valve 22 is not opened as the piston approaches the bottom of the power stroke as is done in conventional engine practice, but instead, the exhaust valve remains closed and the piston construction of the instant invention converts the exhaust gas energy in the form of unburned fuel and elevated temperature and pressure into a force acting to drive the piston.

Since the drawing illustrates adaptation of the invention to a typical gasoline internal combustion engine, a suitable spark plug 25 is shown mounted in head 13 to carry out its normal function of igniting the combustile mixture introduced into the cylinder bore 14 through duct 21, during the intake stroke of piston 15 with valve 20 open.

The piston 15 is connected by an appropriate connecting rod 3% to the crank of a crank shaft 31. This crank shaft transmits the work output from the engine and rotates about an axis 32. The connecting rod will be appropriately constructed to cooperate with the formation of piston 15 as described hereinafter. Thus it may take the form of parallel rods, each connected at its upper end to piston 15 by an appropriate wrist pin 33 and at its lower end to the crank shaft 31 by a crank pin 34. Suitable bearings 35 and 35 may be provided for journaling the wrist pin and crank pin respectively. The piston 15 may be provided with suitable piston rings 37 as is conventional to minimize blow-by between the piston and cylinder bore.

The piston 15 is provided internally with a passage 40 which extends downwardly from an inlet 42 in the upper end wall 41 of the piston. The inlet 42 may be suitably belled at its entrance to promote smooth flow of gases from the cylinder bore 14 into passage 40.

In the embodiment illustrated, the passage 40 termi-' nates in an outlet or exit 43 disposed in the side Wall or skirt of the piston 1.5. The passage 40 includes an exit portion 55 immediately preceding the exit or outlet 43. This exit portion 45 extends inwardly and downwardly from the outlet 43 and decreases in cross sectional area from said outlet inwardly to form an expansion chamber for exhaust gases flowing through passage 40 from cylinder bore chamber 14. The exit portion 45 thus provides by its increasing area and positioning relative to piston 15 a means for creating a high velocity gas jet from the super-atmospheric gases flowing through passage 40 much in the manner that reaction turbine blading by the expansion of gases flowing therethrough creates a jet which reacts against the turbine blading to drive the turbine wheel. In the instant invention, the jet of gases created by their expansion and burning of any unburned fuel through exit portion 45 creates a force which acts downwardly on piston 15 and thereby imparts added driving force through connecting rod 30 to crank shaft 31.

In the embodiment as illustrated, a four cycle internal combustion engine is shown. With such an engine, it will be recognized that the passage 49 should be closed against flow of gases therethrough during the full intake and compression strokes of the engine.

Whereas an opening 56 is provided in sleeve 12 to mate with the outlet 43 of passage 4%} as the piston 15 nears the bottom of its stroke, this opening 5%} is closed during the intake and compression strokes of the engine by a slide valve 51. Slide valve 51 thus cuts off communication of opening 51'? with a passageway 52 formed in the cylinder block 16 as is shown in the position of the valve on the drawing.

Slide valve 51 is mounted in a vertical cavity 53 formed in engine block it behind sleeve 12. The valve has a port 55 generally corresponding in size and configuration to opening 5t and passageway 52 so that when the valve is opened, a through passageway for exhaust gases from passage 40 will be provided. A spring 56 is provided beneath valve 51 to normally urge it upwardly, and retain it in the closed position as shown on the drawing. A push rod 57 is slideably mounted above valve 51 to operate the valve, the upper end of such push rod being engaged by a cam 58 mounted on a cam shaft 59 which cam shaft is driven at a speed related to the operating speed of the engine. A chank shaft to cam shaft drive connection is diagrammatically shown at 60 on the drawing.

In the embodiment diagrammatically illustrated, the cam shaft 59 will operate at half the rotative speed of crank shaft 31. similar to the rotating speed of the cam shaft in a conventional gasoline engine. In the position shown, the cam 53 by continued rotation in the direction of the arrow will commence opening of valve 51. The shape of cam 58 is such that once opening of valve 51 commences, it is rapidly opened to its full extent such that a full passageway for flow of exhaust gases through the reaction exit portion of passage 40 in piston will result to create the maximum driving force applied against the piston. The speed of closing of valve 51 is not as critical since the pressure within the cylinder chamber bore 14 will have been relieved by the time valve 51 is ready to be closed, and accordingly, the valve may be closed at any time before the outlet 43 of the piston starts to open a portion of opening 50 on the following intake stroke of the piston. Thereafter, the valve 51 will be maintained closed during the intake and compression strokes until actuated by cam 58 to open near the end of the next power stroke.

As shown, the opening of valve 51 is set to occur with crank shaft 31 disposed at 45 before bottom dead center. It is considered that opening of the valve and thus commencing the production of the reaction force against piston 15 may best occur at between 30 and 45 before bottom dead center. Under some conditions, it may prove desirable to commence venting the gases earlier than the point as shown or later as when the crank is quite near to bottom dead center. If the valve is opened earlier than 45 before bottom dead center, the propelling action of the high pressure gaseous medium in forcing the piston downwardly may be prematurely interrupted. If the valve 51 is opened too late, the thrust produced by flow of gases through passage 40 will not be applied early enough to achieve any useful result in driving the crank shaft 31.

It will be noted that the opening of valve 51 which places opening 50 and passageway 52 in communication, occurs initially adjacent the top or upper portion of opening 50 and passageway 52.. This particular arrangement is considered desirable in that, with the opening occurring initially at this point, the gas flow through passage 40 and particularly exit portion 45 thereof will have a greater vertical component of movement, such that an improved reaction force against piston 15 Will result to assist in driving the piston.

Although, as illustrated, a single passage 49 is shown in the piston 15 on the drawing, it will be recognized that a plurality of such passages may be formed in the piston, each having the expanding exit portion 45 disposed to create the reaction force against the piston. Where two or more passages 40 are provided in the piston, it will be desirable to direct the exit portions 45 of adjacent passages in essentially opposite directions so that the lateral thrust created from flow of gases through the several exit portions will have the effect of balancing each other and thereby eliminate the lateral force applied to the piston urging it against one particular side of the cylinder bore.

In a two cycle internal combustion engine, the slide valve arrangement as shown on the drawing may be dispensed with since the passage 40 in the cylinder will communicate with the exhaust passageway at the lower end of each power stroke while the combustible mixture is being introduced into the cylinder bore above the piston 15. Also, even in a four cycle engine, many other approaches may be taken to valving the outlet 43 of the piston passage 40 other than the slide valve shown in the drawing. Thus, different types of valve constructions could be employed, or the stroke of the piston might be modified by appropriate mechanism such that a short length stroke would be employed on the intake and compression strokes, and a long length stroke provided for the power and exhaust strokes, the long length stroke causing the outlet 43 to mate with an appropriate exhaust passageway in the wall of the cylinder bore, while the short stroke does not permit such mating.

Also, instead of the outlet 43 exiting through the skirt or side wall of the piston a piston having portions of two different diameters might be provided such that an annular shoulder is formed intermediate the ends of the piston. In such a construction, the outlet 43 would face upwardly and exhaust into a chamber having valved communication with the exhaust passageway. As used in the claims, it is to be understood that reference to the outlet or exit of the piston passage through the side wall or skirt of the piston is intended to embrace the above mentioned alternative since even with this alternative approach the outlet would be at the side of the piston intermediate the upper and lower ends thereof.

It is to be understood that while a particular example or adaptation of the invention in a reciprocating piston engine has been illustrated and described and certain variations in construction discussed hereinabove, innumerable variations in construction may be made within the scope and spirit of the claims to the invention. Thus, within the scope of the claims numerous additions, changes and even omissions of structural detail shown and described herein may be made in carrying out the invention without departing from the spirit thereof.

I claim:

1. In a reciprocating piston engine having a shaft, a piston having an end wall against which gaseous pressure acts to drive said piston, means for connecting said piston to rotate the shaft of said engine upon reciprocatory movement of said piston, a passage formed within said piston extending between an inlet in said end wall and an outlet in the side wall of said piston, said passage including an exit portion immediately preceding said outlet which exit portion expands in cross sectional area toward said outlet, said exit portion of said passage extending laterally within said piston and generally toward said end wall of said piston whereby flow of gases under pressure through said passage from said inlet to said outlet and expansion of such gases within said exit portion will impart a force to assist in driving said piston.

2. In an engine having a cylinder bore closed at one end to define a chamber with a piston reciprocable in said bore to be driven during its power stroke by gaseous pressure within said chamber acting on one end of the piston, said piston having Wall means defining a passage communicating with the interior of the chamber through said one end of said piston to receive exhaust gases from said chamber, said passage having an exit portion increasing in cross sectional area toward the outlet end thereof with Said outlet end opening through the side wall of said piston to be closed by the wall of said cylinder bore during the initial portion of the power stroke, said exit portion being directed generally toward said one end of said piston, and said cylinder bore having a port therein disposed to communicate with said outlet end of said exit portion to receive exhaust gases flowing through said passage.

3. In an engine having a cylinder bore closed at one end to define a chamber with a piston reciprocable in said bore to be driven during its power stroke by gaseous pressure within said chamber acting on one end of the 6 piston, said piston having wall means defining a passage communicating with the interior of the chamber through said one end of said piston to receive exhaust gases from said chamber, said passage having an exit portion increasing in cross sectional area toward the outlet end thereof with said Outlet end opening through the side wall of said piston, said exit portion being directed generally toward said one end of said piston, said cylinder bore having a port therein disposed to communicate with said outlet end of said exit portion to receive exhaust gases flowing through said passage, and valve means associated with said port to effect opening of said port for release of gases therethrough as the piston approaches the end of its power stroke.

4. In a reciprocating piston engine including an engine block with a cylinder bore therein closed at one end to define a chamber and a piston rcciprocable in said cylinder bore to be driven during its power stroke by gaseous pressure within said chamber acting on the end wall of said piston, said piston having wall means defining a passage in said piston, said passage having an inlet opening through said end wall of said piston to receive exhaust gases from said cylinder bore, said passage extending away from said end wall and then curving laterally and back generally toward said end wall to exit through the side of said piston, said passage having an exit portion immediately preceding said exit, said exit portion increasing in cross sectional area as it extends toward said exit, said cylinder bore having a port therein disposed to be covered by the side of said piston during the initial portion of the power stroke and to communicate with said exit of said passage during the later portion of said power stroke for the removal of exhaust gases from said cylinder bore through said passage whereby a force is imparted to said piston to assist driving movement thereof as the gases expand and pass through said passage.

5. A piston for use in a reciprocating piston engine having an engine cylinder bore, said piston having an upper end wall against which gaseous pressure acts to drive the piston when positioned within an engine cylinder bore and a side wall extending downwardly from said upper wall, wall means within said piston defining a passage extending between an inlet in said upper wall and an outlet in said side wall, said passage including an exit portion extending inwardly from. said outlet and downwardly relative to said upper end wall, said exit portion gradually decreasing in cross sectional area from said outlet inwardly to form an expansion chamber for gases flowing through said passage whereby a force is imparted to said piston to assist driving movement thereof as the gases expand and pass through said exit portion to the outlet thereof.

6. A piston for use in a reciprocating piston engine having an engine cylinder bore, said piston having an upper end wall against which gaseous pressure acts to drive the piston when positioned within an engine cylinder bore and a side wall extending downwardly from said upper wall, wall means within said piston defining a passage extending between an inlet in said upper wall and an outlet in said side wall, said passage having an inlet portion which decreases in cross sectional area downwardly to provide for smooth flow of gases through said inlet into said passage, said passage including an exit portion extending inwardly from said outlet and downwardly relative to said upper end wall, said exit portion gradually decreasing in cross sectional area from said outlet inwardly to form an expansion chamber for gases flowing through said passage wherein a force is imparted to said piston to assist driving movement thereof as the gases expand and pass through said exit portion to the outlet thereof.

7. An engine for converting energy in a gaseous motive fluid into usable work comprising a cylinder block having a cylinder bore therein and a cylinder head closing one end of said bore to define a chamber, a piston reciprocable within said bore to be driven during its power stroke by the gaseous motive fluid within said chamber acting on one end wall of said piston, a crankshaft and connecting rod means connecting said piston thereto to drive the crankshaft upon reciprocatory movement of said piston, a passage formed within said piston extending between an inlet in said end wall and an outlet in the side wall of said piston, said passage including an exit portion immediately preceding said outlet which exit portion expands in cross sectional area toward said outlet, said exit portion of said passage extending laterally within said piston and generally toward said end wall of said piston whereby flow of gases through said passage from said inlet to said outlet and expansion of such gases within said exit portion will impart a force to assist in driving said piston, a port in said cylinder bore communicable with said outlet of said passage during the latter portion of said power stroke to receive and convey away exhaust gases flowing through said passage.

8. An engine as recited in claim 7 wherein said port communicates with said outlet when said crankshaft is at approximately 45 to 30 before bottom dead center in the power stroke of said piston.

9. An engine for converting energy in a gaseous motive iluid into usable work comprising a cylinder block having a cylinder bore therein and a cylinder head closing one end of said bore to define a chamber, a piston reciprocable within said bore to be driven during its power stroke by the gaseous motive fluid within said chamber acting on one end wall of said piston, a crankshaft and connecting rod means connecting said piston thereto to drive the crankshaft upon reciprocatory movement of said piston, a passage formed within said piston extending between an inlet in said end wall and an outlet in the side wall of said piston, said passage including an exit portion immediately preceding said outlet which exit portion expands in cross sectional area toward said outlet, said exit portion of said passage extending laterally within said piston and generally toward said end wall of said piston whereby flow of gases through said passage from said inlet to said outlet and expansion of such gases within said exit portion will impart a force to assist in driving said piston, a port in said cylinder bore communicable with said outlet of said passage to receive and convey away exhaust gases flowing through said passage, and valve means associated with said port to effect opening of said port for release of gases therethrough as the piston ap proaches the end of its power stroke.

10. An engine as recited in claim 9 wherein said valve means opens said port when said crankshaft is at approximately 45 to 30 before bottom dead center in the power stroke of said piston.

11. An engine as recited in claim 9 wherein said valve means comprises a. valve member mounted to be movable in a path parallel to the reciprocating path of said piston, and cam means are provided operable in relation to the rotative speed of said crankshaft to move said valve member to open said port as said piston nears the end of its power stroke.

12. An engine for converting energy in a gaseous motive fluid into usable work comprising a cylinder block having a cylinder bore therein, a cylinder head closing the upper end of said bore to define a chamber therein, a piston reciprocable within said bore to be driven during its power stroke by the gaseous motive fluid within said chamber acting on the upper end wall of said piston, a crankshaft and connecting rod means connecting said piston thereto to drive the crankshaft upon reciprocatory movement of said piston, a passage formed within said piston extending between an inlet in said upper end wall and an outlet in the side wall of said piston, said passage including an exit portion extending inwardly from said outlet and downwardly relative to said upper end wall, said exit portion gradually decreasing in cross sectional area from said 13. An engine for converting energy in a gaseous motive fluid into usable work comprising a cylinder block having a cylinder bore therein and a cylinder head closing one end of said bore to define a chamber, a piston reciprocable within said bore to be drivenduring its power stroke by the gaseous motive fluid within said chamber acting on one end wall of said piston, a crankshaft and connecting rod means connecting said piston thereto to drive the crankshaft upon reciprocatory movement of said piston, a passage formed within said piston extending between an inlet in said end wall and an outlet in the side wall of said piston, said passage including an exit portion immediately preceding said outlet which exit portion expands in cross sectional area toward said outlet, said exit portion of said passage extending laterally within said piston and generally toward said end wall of said piston whereby flow of gases through said passage from said inlet to said outlet and expansion of such gases within said exit portion will impart a force to assist in driving said piston, a port in said cylinder bore communicable with said outlet of said passage to receive and convey away exhaust gases flowing through said passage, a valve member mounted to be movable in a path parallel to the reciprocation path of said piston, means biasing said member toward a position closing said port, and means connected to operate said member in timed relation to the rotative speed of said crankshaft, said last named means being operable to initially open the end of said port nearest said cylinder head in relieving exhaust gas flow through said passage and said port.

14. An engine for converting energy in a gaseous motive fluid into usable work comprising a cylinder block having a cylinder bore therein, a cylinder head closing one end of said bore to define a chamber, a piston reciprocable within said bore to be driven during its power stroke by the gaseous motive fluid within said chamber acting on one end wall of said piston, a crankshaft and connecting rod means connecting said piston thereto to drive the crankshaft upon reciprocator'y movement of said piston, an inlet valve for controlling admission during the intake stroke of said piston, an exhaust valve for venting exhaust gases during the exhaust stroke of said piston, means for operating said inlet and exhaust valves in relation to the rotative speed of said crankshaft, a passage formed within said piston extending between an inlet in said end wall and an outlet in the side wall of said piston, said passage including an exit portion immediately preceding said outlet which exit portion expands in cross sectional area toward said outlet, said exit portion of said passage extending laterally within said piston and generally toward said end wall of said piston whereby flow of gases through said passage from said inlet to said outlet and expansion of such gases within said exit portion will impart a force to assist in driving said piston, a port in said cylinder bore communicable with said outlet of said passage to receive and convey away exhaust gases flowing through said passage, and valve means associated with said port to effect opening of said port for release of gases therethrough as the piston approaches the end of its power stroke.

15. An engine as recited in claim '14 wherein said inlet valve controls admission of a combustible mixture into said chamber and spark ignition means is provided within said chamber to ignite the mixture following the compression stroke of said piston.

16. An engine as recited in claim 14 wherein said inlet and exhaust valves and said valve means are operated by cam means driven in relation to the rotative speed of the crankshaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,249,588 Barbour Dec. 11, 1917 

1. IN A RECIPROCATING PISTON ENGINE HAVING A SHAFT, A PISTON HAVING AN END WALL AGAINST WHICH GASEOUS PRESSURE ACTS TO DRIVE SAID PISTON, MEANS FOR CONNECTING SAID PISTON TO ROTATE THE SHAFT OF SAID ENGINE UPON RECIPROCATORY MOVEMENT OF SAID PISTON, A PASSAGE FORMED WITHIN SAID PISTON EXTENDING BETWEEN AN INLET IN SAID END WALL AND AN OUTLET IN THE SIDE WALL OF SAID PISTON, SAID PASSAGE INCLUDING AN EXIT PORTION IMMEDIATELY PRECEDING SAID OUTLET WHICH 